This latest riff on the scorned-ex revenge drama is oddly watchable, but still can never reconcile the disconnect between its two leads.

There are few surprises in “Unforgettable,” the first feature film from longtime producer Denise Di Novi. In hair color, clothing and personality type, the two female leads of this custody-battle-turned-murder-mystery are diametrically opposed at every turn, hurtling toward a final showdown that will probably not end in hugs and an exchange of floral arrangements. But there’s something about the way that Di Novi and writer Christina Hodson never stray from this dynamic that gives the movie a strange heightened, camp-adjacent appeal.

“Unforgettable” treats this central struggle over the heart of a family in the same way that a recent Ken Watanabe character does, by surveying the battlefield and coming to a simple, definitive conclusion: “Let them fight.”

The setup for this feud is as simple as its execution. New SoCal transplant Julia Banks (Rosario Dawson) is fresh off a move from a publishing gig in New York to be with her fiance David (Geoff Stults), a former Wall Street player and new brewery owner. David’s ex-wife Tessa (Katherine Heigl), under the impression that their daughter Lily held the key to repairing their broken marriage, quickly turns to devious ends to make sure that this new relationship does not take permanent hold.

From the outset, Tessa is the archetypal scorned villain. Slowly attending to her hair and makeup with surgical precision as she stares unflinchingly into a mirror, all that’s missing in the announcement of her as the antagonist is Tessa chanting an ominous couplet at her reflection. Heigl is calculated at every turn, calibrating her puppet master persona with such twisted delight, that it’s hard not to want to see her get her own franchise where she solely plays spiteful retribution seekers. Tessa is the kind of character who fancies herself the star in her own revenge fantasy, so Heigl’s mannered approach fits in well with her half of the movie.

This leaves Julia, the would-be stepmother as the heroine, thrust into a series of constant manipulation, while dealing with the memories of a past abusive partner. But instead of being the hapless damsel preyed upon by an evil ex, Julia channels that frustration into dogged determination to protect her new life and the people in it. Even when Julia’s outmaneuvered, Dawson plays her frustration as the only recognizable human in a sea of one-dimensional players. Through Julia, Dawson brings a dose of rationality and complexity to a story dominated by its own oversimplified logic.

Individually, both of these performances are well-suited to these actresses’ strengths. Even in the scenes with just the two of them interacting, they each seem comfortable inhabiting their wildly different roles. But “Unforgettable” has too much fun smashing these two styles together (figuratively and, in an all but inevitable turn, quite literally), while still pretending this drama is anything but a surface-level personality brawl.

Part of the reason that this mismatch never quite lands is that the man they’re fighting over does little to round out the drama. David is a blank slate for each woman to project onto, leaving little but the man himself as the sole overlap in their Venn diagram of desire. Try as Stults might to infuse some charm, David is merely a conduit through which these women engage in a proxy fight.

The rest of the cast are there at Tessa and Julia’s convenience, from Cheryl Ladd’s menacing matriarch to Whitney Cummings as Julia’s boss and confidant. In one scene, Sarah Burns reprises her work as part of the “Big Little Lies” Greek chorus and lays claim to the championship belt of Coastal California gossipers. And poor Lily. David and Tessa’s child quickly becomes the privileged six-year-old’s answer to Job, thrust into a series of escalating, tiny traumas.

The film seems so intent on getting its catfight underway that it dispenses with any backstory subtlety. All relevant information to the lives of the three individuals at the heart of this dangerous tug-of-war is dispensed in not one, but three speeches delivered at corporate celebrations, to a crowd of attentive, anonymous listeners.

Even more amusing are the technology-based contrivances that help Tessa bring about her master plan. Luckily, you don’t dwell on the off-brand Facebook Messenger and the preposterously oversimplified background database because Heigl’s reaction shots are so deliciously diabolical that they devour everything in sight.

Di Novi’s first time in the director’s chair isn’t without some attempts to pull this away from something aggressively standard. For a story set in the sunny climes Southern California, there sure are plenty of metaphor-heavy shadows. And one particular cat burglar sequence that has the audience looking straight through Tessa’s eyes hints that this movie may be more self-aware than it otherwise lets on.

But if there are few frills to be found in “Unforgettable,” it’s understandable that Di Novi would want to clear a wide path for the two performances cutting their way through the story. If only for one particular equestrian center face-off, Heigl and Dawson are reason enough to stick this one out. It’s just hard to shake that they seem to be starring in two different movies.